This invention relates to a process for imparting hydrolysis resistance to rare-earth oxysulfide phosphors by adding zinc to the initial reactant mixture and firing this mixture to form the phosphor.
Rare-earth oxysulfide phosphors have become successful x-ray intensifier phosphors. In this application the phosphor is applied to an organic film or substrate which forms the basis of an intensifier screen. The screen is mounted in a cassette where in operation the phosphor thereon is exposed to x rays. The phosphor converts the x rays into visible or near-visible radiation to which a photosensitive film is exposed resulting in an image being produced on the film.
One of the problems that has developed in the above application is that if the phosphor comes in contact with water, hydrolytic reaction can occur and hydrogen sulfide is released. Additionally, if water is inadvertently dropped on an intensifier screen in an x-ray cassette and a film is placed in the cassette, a reaction between hydrogen sulfide and the silver halide in the film emulsion occurs. This reaction can cause a discoloration on the intensifying screen which in turn can degrade radiographic image quality.